Retention of a polishing pad on a platen

ABSTRACT

A polishing pad is retained on a platen by structures which do not require adhesive. In one embodiment, a polishing pad has a top polishing surface and an undersurface. The undersurface has a surface profile which is configured to interfit with a complementary surface profile on a platen. The surface profile of the undersurface may comprise an array of parallel ridges and grooves.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to device and method for securing a polishing pad on a platen of a polishing apparatus.

[0003] 2. Discussion of Related Art

[0004] Polishing pads for removing material from the surface of a workpiece are well-known. A typical polishing pad is a relatively thin, disk-shaped article that is mounted on a platen of a polishing machine. The polishing pad is generally secured to the platen by a pressure sensitive adhesive that is laminated on the back side of the polishing pad.

[0005] The pressure sensitive adhesive has a number of disadvantages. First, as the polishing pad is placed on the platen, bubbles of air tend to get trapped between the adhesive and the platen. Any trapped air will distend the relatively thin polishing pad, thereby causing raised areas or bulges in the polishing surface of the polishing pad. These bulges cannot be eliminated by forcing the air bubbles out from under the pad with a roller. Instead, the bulges must be manually pierced with a hand tool in order to let the trapped air escape, and then the pad material can be pressed flat against the platen to obtain the flatest possible polishing surface. This is a time-consuming process, and some small bulges often go undetected and remain in the polishing surface. Any bulges in the polishing surface will generate non-uniformities on the polished surface of the workpiece, thereby causing defects in the polished surface.

[0006] Another problem associated with the adhesive is that considerable force is required to pull a used polishing pad up from the platen for replacement, which work leads to strain injury to personnel. Also, adhesive residue normally remains on the platen after the old polishing pad is pulled off. The adhesive residue must be removed with a solvent. Removing the residue is a time-consuming process which exposes personnel to potential chemical hazards.

[0007] Another problem is that the adhesive may release sodium and other ion bearing elements which interfere with semiconductor processing.

[0008] There is a need for a device for securing a polishing pad to a platen which overcomes these problems.

SUMMARY OF THE INVENTION

[0009] The invention provides devices for securing a polishing pad to a platen without any adhesive.

[0010] According to the invention, a polishing apparatus comprises a platen having a front face and a surface profile on the front face. A polishing pad has a top polishing surface and an undersurface with a surface profile which is configured to interfit with the surface profile on the platen.

[0011] In one embodiment, the surface profile of the undersurface comprises an array of parallel ridges and grooves.

[0012] According to another aspect of the invention, a polishing pad is adhered to a platen by a vacuum that is communicated through a microporous material.

[0013] According to another aspect of the invention, a polishing pad is adhered to a platen by capillary attraction of a liquid that is disposed between non-porous polymeric surface layers.

[0014] According to another aspect of the invention, a polishing pad is adhered to a platen by electrostatic forces between polymeric surface layers.

[0015] According to another aspect of the invention, a polishing pad is adhered to a platen by a vacuum and is further stabilized by at least one of pins and texture on the front face of the platen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention will now be described by way of example with reference to the accompanying drawings wherein:

[0017]FIG. 1 is a side elevation view of a polishing pad which is spaced above a platen;

[0018]FIG. 2 is an enlarged view of portions of the polishing pad and the platen which are enclosed by phantom lines 2 in FIG. 1;

[0019]FIG. 2A is an enlarged view of the polishing pad and the platen showing confronting textured surfaces;

[0020]FIG. 3 is a bottom view of the portion of the polishing pad which is shown in FIG. 2;

[0021]FIG. 4 is an enlarged view of the polishing pad and the platen showing the widths of the grooves and ridges decreasing radially from the center of the pad and the platen;

[0022]FIG. 5 is an enlarged view of the polishing pad and the platen showing grooved cover layers on the pad and the platen;

[0023]FIG. 6 is a side view of the polishing pad being held on the platen by a vacuum generator;

[0024]FIG. 7 is an enlarged view of the polishing pad and the platen showing confronting non-porous, polymeric surface layers with a liquid disposed there between;

[0025]FIG. 7A is an enlarged view of the polishing pad and the platen showing a liquid layer disposed between the front face of the platen and a polymeric surface layer on the polishing pad;

[0026]FIG. 8 is an enlarged view of the polishing pad and the platen showing confronting electrostatic, polymeric surface layers;

[0027]FIG. 9 is a side view of the polishing pad being held on the platen by a vacuum generator, wherein pins extend from the front face of the platen; and

[0028]FIG. 10 is an enlarged view of the polishing pad engaged with a platen having directionally oriented pins extending from the front face of the platen.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0029] There is shown in FIG. 1 a polishing pad 10 comprising a top polishing surface 12 and an undersurface 14 that is adapted to be mounted on a front face 16 of a platen 18. The undersurface 14 has a profiled surface which is configured to interfit with a complementary profiled surface on the front face 16 of the platen.

[0030] In a preferred embodiment as shown in FIGS. 2 and 3, the undersurface 14 has a surface profile which includes an array of parallel ridges 22 and grooves 24, and the front face 16 has a surface profile which includes a complementary array of parallel ridges 26 and grooves 28. The ridges 22 and the grooves 24 are configured to interfit with the grooves 28 and the ridges 26, respectively, when the polishing pad is mounted on the platen.

[0031] The ridges 22, 26 are dimensioned for a close slip fit in respective ones of the grooves 24, 28. Preferably, the width of ridges 22, 26 differs slightly from the width of grooves 24, 28 in order to provide room for the ridges and grooves to cooperatively mate. More specifically, the difference in widths of each corresponding, mating pair of ridges and groves preferably is less than about 5 percent of the width of the larger of the pair. Likewise, preferably the height of ridges 22, 26 differs slightly from the depth of grooves 24, 28. More specifically, the difference in height of the ridge and depth of the groove of each corresponding, mating pair of ridges and groves preferably is less than about 5 percent of the larger height or depth of the pair. The width and height of ridges and the width and depth of grooves may vary across the surface (in contrast to being uniform) so long as mating pairs of ridges and grooves have corresponding dimensions. As shown in FIG. 4 for example, the widths of the ridges 22, 26 and grooves 24, 28 decrease radially outward from the center of polishing pad 10 and platen 18. In a preferred embodiment, the ridges and grooves are of uniform width, height and depth as shown in FIG. 2, wherein each of the ridges 22, 26 has a height of 0.025 inch and a width of 0.090 inch, and each of the grooves 24, 28 has a depth of 0.025 inch and a width of 0.095 inch, which provides a ridge/groove width differential of (0.095−0.090)/0.095×100=about 5.3%.

[0032] In a preferred embodiment, the polishing apparatus is configured for chemical mechanical polishing (CMP), wherein the platen and the polishing pad are rotated together and positioned beneath the material to be polished (typically a semiconductor substrate or workpiece such as silicon, germanium, or gallium arsenide), and the material to be polished is lowered onto the rotating polishing pad from above. During a polishing operation, the polishing pad experiences a downward normal force as a workpiece (not shown) is urged against the polishing surface 12 of the polishing pad, and the polishing pad experiences frictional forces which are generated by rotation of the workpiece and rotation of the platen and polishing pad combination. Due to the interfitting nature of the ridges and grooves, the polishing pad exerts a grip on the platen, which grip cannot be overcome by ordinary frictional forces which are generated on the pad. Thus, the polishing pad is retained on the platen in the absence of any extraordinary forces, without using an adhesive. As an added benefit, no contaminants such as ions or chemically active compounds are released from an adhesive in the semiconductor polishing process.

[0033] It should be understood that complementary profiled surfaces according to the invention may encompass patterns, textures, and shapes other than parallel ridges and grooves, and may encompass barb-like pins formed from the same material as the remainders of the pad material and platen material to provide the profiled surfaces, and may encompass barb-like pins that are separate structures that are mounted on the pad material and the platen material to provide the profiled surfaces. For example, the surfaces 14 and 16 may have complementary surface profiles of interfitting elements in patterns such as radial, sine wave, square wave, V-shape, or any other regular or irregular pattern. The interfitting elements may have shapes such as elongated linear shape, circular, square, or any other regular or irregular polygon shape, and all such patterns and shapes are considered to be within the scope of the invention. The interfitting elements may be textured, for example with a roughened surface texture, to increase the frictional forces between the polishing pad and the platen. As shown in FIG. 2A, the complementary surface profiles may be comprised of surface texturing on the undersurface 14 of the polishing pad 10 and the front face 16 of the platen 18, with the surface texturing itself comprising the interfitting elements.

[0034] A surface profile for the polishing pad 10 may be formed integrally in a polishing material layer, as shown in FIG. 2. In a preferred embodiment the polishing material is a microporous urethane material such as an IC1000 polishing pad available from Rodel Inc., and ridges and groves are lathed directly into the polishing material. Alternatively as shown in FIG. 5, the surface profile may be formed on a separate cover layer 11 which is laminated to the polishing material layer 12. Similarly, a surface profile on the platen may be integrally formed in the platen 18 as in FIG. 2 or may be formed on a separate cover layer 17 which is laminated to the platen 18 as in FIG. 5. In another embodiment, cover layers 11 and 17 comprise hook and loop fastener layers such as the type commonly referred to as Velcro®. The surface profile may be applied during manufacturing of the polishing pad or platen, for example during pressing or dye casting, or applied post-manufacture, for example by machining such as lathing or routering.

[0035] A used polishing pad can easily be removed from the platen by lifting up an edge of the polishing pad and pulling back the polishing pad with a peeling motion until the entire pad is separated from the platen. A new polishing pad can be installed on the platen by aligning the ridges with corresponding grooves and by mildly urging the ridges and grooves into engagement.

[0036] According to another embodiment of the invention shown in FIG. 6, a polishing apparatus includes a polishing pad 10 and a platen 18 made of microporous material such as a porous metal. Microporous material is characterized by air permeability through the material. The material includes a network of microfine pores which are formed in situ during manufacture of the material. The pores provide conduits for the passage of air. Preferably, the pores have a diameter of less than 100 microns. Thus, the pores are substantially smaller than any apertures which could be formed in a solid material by traditional manufacturing techniques.

[0037] The platen 18 has a front face 16, sides 21, and a back face 19, and the undersurface 14 of the polishing pad 10 is supported on the front face. A vacuum generator 30 is connected for applying a vacuum (represented by arrow 32) to the microporous material at the back face of the platen. The vacuum is communicated through the microporous material to the front face of the platen, thereby adhering the polishing pad to the front face. Preferably, a directional-flow microporous material is used wherein the pores are aligned and structured such that the vacuum applied to the back face of the platen is communicated to the front face but not to the sides of the platen.

[0038] Advantageously, the vacuum will not be exhibited on localized areas of the polishing pad as would occur with a platen having apertures or vacuum holes, which would tend to cause depressions in the polishing surface at the localized areas. Instead, the vacuum will be substantially evenly distributed across the entire face of the polishing pad due to the microfine pores.

[0039] In another embodiment shown in FIG. 7, the polishing pad 10 is secured to the platen 18 by capillary action. In this embodiment, the platen and the polishing pad each include a surface layer 34 and 36, respectively, comprising a non-porous polymeric film. Preferred polymeric films are polypropylene and polytetrafluoroethylene (PTFE). The surface layers 34 and 36 of the platen and the polishing pad are arranged in confronting relationship. Alternatively, as shown in FIG. 7A, the polymeric surface layer may be omitted from the front face 16 of the platen 18 where the surface of the platen is sufficiently smooth to enable the desired capillary action between liquid layer 38 and the surface layer 36 of the polishing pad.

[0040] A liquid is disposed in a layer 38 between the polymeric film surface layers. The liquid must be able to wet both surface layers. Relative wetness of a liquid on a particular surface can be defined by a contact angle which the liquid makes with that surface. For the present invention, a suitable liquid will have a contact angle with each of the surface layers which is preferably less than 90°, more preferably less than 60°, and even more preferably less than 30°. The liquid layer exhibits a capillary attraction for the surface layers which keeps the polishing pad adhered to the platen during a polishing operation. The liquid should have a relatively low vapor pressure to minimize evaporation.

[0041] In another embodiment shown in FIG. 8, the polishing pad 10 is secured to the platen 18 by static cling. The polishing pad and the platen each include a surface layer 38 and 40, respectively, comprising a polymer that can hold a static charge (i.e., an electrostatic polymer). Preferably, the electrostatic polymer has a dielectric constant which is greater than 2.4. Preferred electrostatic polymers for this invention are polyvinylchloride (PVC), Mylar® polyester film, or polyvinylidene fluoride. When the surface layers 38, 40 of the polishing pad and the platen are in contact with each other, electrostatic forces between the surfaces will keep the polishing pad adhered to the platen.

[0042] In another embodiment shown in FIG. 9, the polishing pad 10 is secured to the platen 18 by a vacuum and is additionally stabilized by pins 42 or texture on the front face 16 of the platen. The polishing pad is disposed on the front face of the platen. The platen includes at least one aperture 44 extending between the front face 16 of the platen and the back face 19 of the platen. Alternatively, the platen can be made from a microporous material as discussed previously. A vacuum generator 30 is connected for applying a vacuum (represented by arrow 32) to the back face of the platen, which is communicated through the at least one aperture (or alternatively the microporous material) to the front face of the platen. The polishing pad is adhered to the front face of the platen by the vacuum. Additionally, the front face of the platen includes small pins 42 or surface texture which serve to increase frictional forces between the polishing pad and the platen, thereby helping to resist rotation or translation of the polishing pad over the platen when the polishing pad is rubbed against a workpiece. The pins or surface texture may be directionally oriented to oppose reaction forces which are generated on the polishing pad due to interaction between the polishing pad and the workpiece during a polishing operation. The surface texture may include surface profiles such as those shown in FIGS. 2, 2A, 3, 4, and 5, and discussed previously.

[0043] In another embodiment shown in FIG. 10, the polishing pad 10 is secured to the platen 18 by pins 42 or texture on the front face 16 of the platen. The polishing pad is disposed on the front face of the platen and the undersurface 14 of the polishing pad is deformed or penetrated by the pins 42 or texture on the front face of the platen. The undersurface 14 may be the same material as the polishing surface, provided that the material is readily deformed or penetrated for engagement to the platen, otherwise the undersurface may to covered with a layer such as, a polymer film or wax that is readily deformed or penetrated. The polishing pad is held in place by gravitational forces and the normal force of the polishing pad rubbed against a workpiece. Pins 42 or surface texture on the platen serve to increase frictional forces between the polishing pad and the platen, thereby helping to resist rotation or translation of the polishing pad over the platen when the polishing pad is rubbed against a workpiece. As shown in FIG. 10, the pins or surface texture may be directionally oriented to oppose reaction forces which are generated on the polishing pad due to interaction between the polishing pad and the workpiece during a polishing operation.

[0044] In additional embodiments, the features of the various embodiments discussed previously may be combined. For example, the embodiments of FIGS. 6, 7, and 8 may be modified to include surface profiling as shown in FIGS. 2, 2A, 3, 4, 5, 9, and 10. In the embodiment of FIG. 6, the undersurface 14 of the polishing pad 10 and the front face 16 of the platen 18 may be modified as shown in FIGS. 2, 2A, 3, 4, 5, 9, and 10. Cover layers 11 and 17 in the embodiment shown in FIG. 5 may comprise a non-porous polymeric film with a liquid disposed there between (as shown by layers 36 and 34, respectively, in FIG. 7) or may comprise an electrostatic polymer (as shown by layers 38 and 40, respectively, in FIG. 8). 

We claim:
 1. A polishing pad which can be mounted on a platen, the polishing pad comprising: a top polishing surface and an undersurface, the undersurface having a surface profile which is configured to interfit with a complementary surface profile on the platen.
 2. The polishing pad of claim 1 wherein the surface profile of the undersurface comprises an array of parallel ridges and grooves.
 3. The polishing pad of claim 2 wherein the difference in widths of each ridge or groove on the polishing pad forming a mating pair with a corresponding groove or ridge on the platen is less than about 5 percent of the width of the larger of the pair.
 4. The polishing pad of claim 2 wherein each of the ridges has a height of about 0.025 inch and a width of about 0.090 inch and each of the grooves has a depth of about 0.025 inch and a width of about 0.095 inch.
 5. The polishing pad of claim 1 wherein the surface profile of the undersurface comprises a portion of a hook and loop fastener.
 6. The polishing pad of claim 1 wherein the surface profile of the undersurface comprises a textured surface.
 7. A platen for receiving a polishing pad, the platen comprising a front face having a surface profile which is configured to interfit with a complementary surface profile on the polishing pad.
 8. The platen of claim 7 wherein the surface profile of the front face comprises an array of parallel ridges and grooves.
 9. The platen of claim 8 wherein the difference in widths of each ridge or groove on the platen forming a mating pair with a corresponding groove or ridge on the polishing pad is less than about 5 percent of the width of the larger of the pair.
 10. The platen of claim 8 wherein each of the ridges has a height of about 0.025 inch and a width of about 0.090 inch and each of the grooves has a depth of about 0.025 inch and a width of about 0.095 inch.
 11. The platen of claim 7 wherein the surface profile of the front face comprises a portion of a hook and loop fastener.
 12. The platen of claim 7 wherein the surface profile of the front face comprises a textured surface.
 13. A polishing apparatus comprising: a platen having a front face and a surface profile on the front face; and a polishing pad having an undersurface with a surface profile which is configured to interfit with the surface profile on the platen.
 14. The polishing apparatus of claim 13 wherein the surface profiles comprise an array of parallel ridges and grooves.
 15. The polishing apparatus of claim 14 wherein the difference in widths of each ridge or groove on the platen forming a mating pair with a corresponding groove or ridge on the polishing pad is less than about 5 percent of the width of the larger of the pair.
 16. The polishing apparatus of claim 14 wherein each of the ridges has a height of about 0.025 inch and a width of about 0.090 inch and each of the grooves has a depth of about 0.025 inch and a width of about 0.095 inch.
 17. The polishing apparatus of claim 13 wherein the surface profiles comprise a hook and loop fastener.
 18. The polishing apparatus of claim 13 wherein the surface profiles comprise textured surfaces.
 19. A platen for receiving a polishing pad, the platen comprising a microporous material.
 20. A polishing apparatus comprising: a platen comprising microporous material, the platen having a front face and a back face; a polishing pad in contact with the front face; and a vacuum generator connected to the back face for applying a vacuum to the microporous material, wherein the vacuum is communicated through the microporous material to the front face, thereby adhering the polishing pad to the front face.
 21. The polishing apparatus of claim 20 further comprising a surface profile on the front face of the platen; and a surface profile on the undersurface of the polishing pad which is configured to interfit with the surface profile on the platen.
 22. A polishing pad comprising a top polishing surface and a non-porous polymeric undersurface for attachment to a platen.
 23. A platen comprising a non-porous polymeric front face for receiving a polishing pad.
 24. A polishing apparatus comprising: a platen having a front face, a polishing pad having a non-porous polymeric surface layer arranged in confronting relationship to the front face of the platen; and a liquid layer disposed between the front face of the platen and the surface layer of the polishing pad, wherein the polishing pad is adhered to the platen by capillary attraction of the liquid layer for the front face and the surface layer.
 25. The polishing apparatus of claim 24 wherein the front face of the platen has a non-porous polymeric surface layer, and the liquid layer is disposed between the surface layer of the platen and the surface layer of the polishing pad.
 26. The polishing apparatus of claim 25 further comprising a surface profile on the surface layer of the platen; and a surface profile on the surface layer of the polishing pad which is configured to interfit with the surface profile On the platen.
 27. A polishing pad comprising a top polishing surface and a electrostatic polymeric undersurface for attachment to a platen.
 28. A platen comprising an electrostatic polymeric front face for receiving a polishing pad.
 29. A polishing apparatus comprising: a platen and a polishing pad each having a polymeric surface layer which can hold a static electrical charge, the surface layers being in contact with each other, wherein the polishing pad is adhered to the platen by electrostatic forces between the surface layer of the polishing pad and the surface layer of the platen.
 30. The polishing apparatus of claim 29 further comprising a surface profile on the surface layer of the platen; and a surface profile on the surface layer of the polishing pad which is configured to interfit with the surface profile on the platen.
 31. A platen comprising a textured front face for receiving a polishing pad.
 32. The platen of claim 31 wherein the texture is arranged to offset a rotational force produced when the polishing pad is applied to a workpiece.
 33. A platen comprising a front face having a plurality of pins extending therefrom for engaging the undersurface of the polishing pad.
 34. The platen of claim 33 wherein the pins are arranged to offset a rotational force produced when the polishing pad is applied to a workpiece.
 35. A polishing apparatus comprising: a platen comprising an air-permeable material, the platen having a back face and a textured front face; a polishing pad having an undersurface in contact with the front face; and a vacuum generator connected to the back face for applying a vacuum through the air-permeable material, wherein the vacuum is communicated through the air-permeable material to the front face of the platen, thereby adhering the polishing pad to the platen and the texture on the front face additionally stabilizing the polishing pad.
 36. The polishing apparatus of claim 35 wherein the air-permeable material is a microporous material.
 37. The polishing apparatus of claim 35 wherein the air-permeable material is a material comprising at least one aperture connecting the back face and the front face.
 38. The polishing apparatus of claim 35 wherein the texture on the front face of the platen is arranged to offset a rotational force produced when the polishing pad is applied to a workpiece.
 39. The polishing apparatus of claim 35 wherein the undersurface of the polishing pad is capable of being deformed or penetrated by the textured front face of the platen.
 40. A polishing apparatus comprising: a platen comprising an air-permeable material, the platen having a back face and a front face comprising a plurality of pins extending therefrom; a polishing pad having an undersurface in contact with the front face; and a vacuum generator connected to the back face for applying a vacuum through the air-permeable material, wherein the vacuum is communicated through the air-permeable material to the front face of the platen, thereby adhering the polishing pad to the platen and the pins on the front face additionally stabilizing the polishing pad.
 41. The polishing apparatus of claim 40 wherein the air-permeable material is a microporous material.
 42. The polishing apparatus of claim 40 wherein the air-permeable material is a material comprising at least one aperture connecting the back face and the front face.
 43. The polishing apparatus of claim 40 wherein the pins on the front face of the platen are arranged to offset a rotational force produced when the polishing pad is applied to a workpiece.
 44. The polishing apparatus of claim 40 wherein the undersurface of the polishing pad is capable of being deformed or penetrated by the pins. 